In the past, much time, effort, and other valuable resources, have been expended in the development of animal litter, particularly for household pets, and especially cats. A material most widely utilized in animal litter is generally clay.
Clay particles provide small animals with dry, sanitary, dustless and relatively odorless litter. Clay materials are sorptive minerals characterized by low bulk density and layered lattice crystal structures. These minerals are derived from condensed forms of silicic acid, H.sub.4 SiO.sub.4, where each silicon atom is surrounded by four oxygen atoms inducing a tetrahedral structure. Chains or two-dimensional sheets are formed when the tetrahedral structures are linked together by the sharing of common oxygen atoms. Clay materials are composed of such silica tetrahedral sheets with a central alumina octahedral sheet.
Through formational mismatching and distortion between the tetrahedral layers and impurities, diverse morphological and chemical properties are conferred to the clay. The absorption of water is one such phenomenon. Clumps of wetted litter permit easy and selective removal of odor-producing animal wastes for convenient disposal without having to replace the entire litter bed.
The irregular series of layers with corresponding interstitial space comprise pores. It is those spaces and pores which give clay its capacity to absorb and store water.
Another material that has found wide acceptance, particularly in clumping litter, is a swelling clay such as sodium (Na) bentonite. However, until the present invention, important nuances of sodium bentonite were either disregarded, unappreciated, or unforeseen by those skilled in the particular art.
Interparticle interaction enables sodium bentonite to clump. In order to clump properly the particles of sodium bentonite must be allowed to interact with one another. To insure such interaction is capable of taking place those skilled in the art have used weight percentages of sodium bentonite well in excess of 60 percent. This is, in part, because animal litter developers have in the past used blends of sodium bentonite and a non-clumping clay material in weight-to-weight ratios. However, a good clumping performance with a composition containing sixty-percent (60%) by weight or less of sodium bentonite heretofore was not readily attainable.
For example, U.S. Pat. No. Re. 33,983 and U.S. Pat. No. 5,503,111 to Hughes, each describe a method and composition for absorbing animal dross using at least about 65 percent by weight of water-swellable bentonite clay, based on the total amount of litter used.
Other clumping agents used in the prior art include polysaccharides, water-soluble gums, dry particulate cellulosic ethers and water-absorbent polymers. These additives require careful handling during manufacture, multiple processing steps and are costly. Further, in such animal litter, the dry particulate cellulosic ethers or the water-absorbent polymers tend to segregate from the particulate clay during handling and shipping because of differences in specific gravity.
Some prior attempts also have been made to overcome the shortcomings of swelling clays by utilizing non-swelling clay and starch as a binder, but such litters were slow clumping. For example, U.S. Pat. No. 5,094,189 to Aylen et al., describes a sorbent, non-swelling clay mixed with 0.2 to 2 percent pregelatinized, cationic starch binder but adhesion of the wetted agglomerates was fairly light and required a day or so to become fairly firm. Likewise, U.S. Pat. No. 5,176,107 to Buschur describes a sorbent, non-swelling clay litter composition utilizing 8 to 14 percent wheat starch paste as a liquid-activated adhesive binding agent which required several hours for the wetted clumps to harden fully. The inability to rapidly remove wetted clumps of animal waste to reduce or eliminate malodors associated therewith from the litter is undesirable.
The clumping effect of the present invention, as previously stated, is related to the interparticle interaction of the sodium bentonite material, particularly with the introduction of moisture.
Montmorillomite is the principal clay mineral of bentonite rock which originates from volcanic ash. Van Olphen, H., An Introduction to Clay Colloid Chemistry, 2nd ed., Wiley-Interscience Publication (1977); p.67. The ion rich composition of the wet material reduces the repulsion forces between the particles allowing the attractive forces--predominantly van der Waals forces, which are not affected by the ion concentration--to dominate. The result is, of course, clumping of the composition with the introduction of water. To increase the clumping effect, it was believed, would necessarily require an increase in the sodium bentonite amount which could interact. It has now been found that that is not necessarily the case.